Abstract
Abstract. A data set of the Cluster cusp crossings over a 5-year period is studied for the interhemispheric comparison of the dipole tilt angle effect on the latitude of the mid-altitude cusp. The result shows that the dipole tilt angle has a clear control of the cusp latitudinal location. Although, the northern cusp moves 0.054° ILAT for every 1° increase in the dipole tilt angle at the mean altitude of 5.2 RE, the southern cusp moves 0.051° ILAT for every 1° increase in the dipole tilt angle at the mean altitude of 6.6 RE. The northern cusp dependence agrees with the trend formed by other observations of different satellites for different altitudes, whereas the southern cusp does not. We therefore suggest that there is an inter-hemispheric difference in the dipole tilt angle dependence of cusp, latitudinal location, which has an impact on other observations of different satellites in different altitudes.
Highlights
The magnetosheath plasma can directly access the highlatitude ionosphere through the two narrow funnel-shaped cusp regions (Heikkila and Winningham, 1971; Frank, 1971)
A survey of the cusp crossings observed by DMSP F7 (∼800 km of altitude) has shown that the cusp is found to move by ±2◦ magnetic latitude (MLAT) from the mean position, which is located between 75.9◦ and 76.8◦ MLAT, in response to the changing dipole tilt angle (Newell and Meng, 1989)
Point 1 is from Newell et al (2006), point 2 from Pitout et al (2006), point 3 from Zhou et al (1999) and points 4 and 5 are from Nemecek et al (2000)
Summary
The magnetosheath plasma can directly access the highlatitude ionosphere through the two narrow funnel-shaped cusp regions (Heikkila and Winningham, 1971; Frank, 1971). Nemevek et al (2000) found the footprint positions of the cusp-like plasma, which is determined by the observation of the MAGION-4 satellite (altitudes 5 to 15 RE), to have a substantial latitudinal dependence on the dipole tilt angle with a slope of 0.15◦ MLAT per 1◦ of dipole tilt angle. In a recent paper, Pitout et al (2006) conducted a statistical study of the four years Cluster crossings of the mid-altitude cusp Their results showed that an increase of ∼11◦ in dipole tilt angle results in an increase of 1◦ in ILAT. Newell et al (2006) checked the difference between the two hemispheres in the dipole title angle effect by the DMSP satellite observations at the ∼800 km altitude They gave a slope of 0.043◦ cusp latitude per 1◦ dipole tile angle by a large number of cases (1857), mostly from the Southern Hemisphere. Our results suggest an inter-hemispheric asymmetry of the dipole tilt angle effect on the latitude location
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